In a blow-moulding machine, the container blank is a previously injected preform.
It is known to manufacture containers, in particular bottles, from thermoplastic materials such as for example polyethylene terephtalate (PET), by stretch-blow moulding of preforms placed inside a mould, the moulding cavity of which is in the shape of the recipient to be obtained.
To this end, preforms having the shape of a cylindrical tube closed at one end and the other end of which is open, constituting the mouth of the bottle to be obtained, are raised, in a thermal conditioning station, to a temperature such that they can be shaped.
The hot preforms are then transferred into a mould constituted by two assembled half-moulds where they are stretched and blown, the blowing being carried out by means of a pressurized gaseous fluid, generally air.
The pressures used during the blowing frequently reach 40 bars. As a result, during manufacture of a bottle of 1.5 liter capacity which has a projected area of approximately 250 cm2, a force of the order of 9.800 decanewtons tends to separate the two assembled half-moulds which constitute the blowing mould.
The applicant's document FR 2793722 discloses an example of a carousel type blow-moulding machine comprising a combined “clamshell” closing and locking mechanism of a moulding unit.
The attached FIG. 1 illustrates this prior art diagrammatically. Two mould supports 1 are articulated to a base 2, integral with a rotor driven rotatably about a shaft 3.
The rotor comprises several identical moulding units distributed in angular fashion about the rotation axis 3.
In the open position, the mould is open radially to the outside and the container blank can be engaged between the two half-moulds, i.e. along the axis 4 of the mould, i.e. in a direction oriented substantially radially from the outside toward the inside.
The moulding unit is opened by pulling the supports 1 radially toward the inside of the carousel.
For this purpose, the moulding unit comprises a slider 5 which slides on the base 2 in a radial direction between a retracted opening position and a forward closing position.
Each moulding unit is provided with two connecting rods 6. Each connecting rod 6 connects a support 1 in articulated fashion to the slider 5.
In the closed position of the moulds, the orientation of the connecting rods 6 is substantially perpendicular to the joining plane of the two half-moulds.
In the closed position of the moulds, the orientation of the connecting rods 6 is substantially perpendicular to the radial direction of sliding movement of the slider 5.
The slider 5 is moved between its forward and retracted positions by a device which combines on the one hand an actuator 7 such as a double-action jack and on the other hand a cam device 8 and cam follower 9.
The actuator 7 is oriented radially with respect to the rotor of the machine. The piston 10 of the actuator 7 is always at the same distance from the rotation shaft of the rotor, while the body 11 of the actuator 7 is capable of tracking the radial movements of the slider 5.
The slider 5 carries the roller 9 which is mounted rotatable about a vertical axis and cooperates with the fixed cam 8 provided on part of the periphery of the rotor.
The cam 8 is arranged radially to the outside with respect to the roller 9. It thus comprises a circular central section 12 of which the axis is identical to that of the shaft 3 of the rotor and which has a radius RI.
On each side of the rotor, an engagement section 13 and a disengagement section 14 are provided.
The engagement section 13 is situated before the central section 12 on the trajectory of the rotor, thus that of the roller 9.
The engagement section 13 makes it possible to bring the roller 9 radially inwards from a radius R2, which is greater than the radius RI and which corresponds to the forward closure position of the slider 5, down to the radius R1 which corresponds to the opening position of the slider 5.
In the following paragraphs of the description of the state of the art, the above mentioned actuator 7 will be a double-action jack.
The cam 8 extends in total only over a sector of approximately 90° about the rotation axis 3 of the rotor.
When the moulding unit in question is not opposite the cam 8, the jack 7 is fed with fluid so that the slider 5 is pushed towards the outside of the carousel, causing the two half-moulds to close against each other.
Just before the blow moulding unit arrives opposite the cam 8, the two chambers of the jack 7 are fed at the same fluid pressure.
Thus, when the roller 9 makes contact with the engagement section 13 of the cam 8, the force exerted by the jack 7 is weak enough to allow the cam 8 to push back the slider 5 towards the inside of the carousel without causing a significant jerk.
The compression of the air contained in the outside chamber of the jack 7 must be such that the jack continues to exert a degree of force on the slider 5, in order to hold the roller 9 onto the cam 8 without it rebounding.
When the roller 9 reaches the central section 12 of the cam 8, the slider 5 has reached its most retracted position and the moulding unit is completely open.
When the roller 9 reaches the disengagement section 14 of the cam 8, the force exerted by the jack 6 must be kept sufficient to ensure that the slider 5 is brought radially outwards and the resultant closing movement of the moulding unit proceeds smoothly without excessive force.
When the roller 9 has passed the end of the disengagement section 14, the moulding unit is then in the closure position and it is then possible to feed only the outside chamber of the jack 7 to avoid any recoil of this jack 7.
The machine described in the document FR 2793722 is perfectly satisfactory but nevertheless does have drawbacks.
Firstly, the movements of the slider 5 which govern the clamping force of the moulds, as well as their opening/closing, depends in particular on the operating pressure in the jack 7. It is difficult to control the pressures in each jack 7 during the rotation of the moulding units.
Secondly, the configuration of the machine disclosed in the document FR 2793 722, is not compact.
The document FR 2 825 659 describes a carousel of an injection moulding or blow moulding machine as shown in FIG. 2.
Each half-mould 1′, 1″ is articulated by means of a connecting rod 3a, 3b to a part 4a, 4b which is mounted pivotable about a shaft 5a, 5b. 
The pivoting parts 4a, 4b are each rotated by an actuating rod 6a, 6b articulated by its ends respectively to said piece 4a, 4b and to a translatory carriage.
A translatory movement of the carriage, using the rods 6a, 6b, causes the parts 4a, 4b to pivot and thus the moulds to open or close by the action of the connecting rods 3a, 3b on the half-moulds 1′, 1″, the pivot shafts 20, 5a and 5b being fixed with respect to the movement of the carriage 7.
To actuate the carriage, a push-pull rod 21, articulated on the one hand to said carriage and on the other hand to a link 22 which is mounted pivotable about a shaft 23 and which is provided with a shaft roller 23. The roller is intended to cooperate with a cam 24, in order to open and close the moulds.
The structure described in the document FR 2825659 is not compact. The applicant has endeavoured to resolve the problems mentioned above.